rule

A rule is a regulation or direction for doing some particular activity. If you have a "no shoes" rule at your house, it means everyone has to take them off at the door.

Other than laws or conditions about what can't and can't be done, rules can be tried-and-true tips like a grammar rule about subject-verb agreement or a spelling rule about making a singular noun plural. Rule can also pertain to power — how someone handles it or how long it lasts, like the peaceful rule of a king whose rule lasted 50 years.

the rule that police (when interrogating you after an arrest) are obliged to warn you that anything you say may be used as evidence and to read you your constitutional rights (the right to a lawyer and the right to remain silent until advised by a lawyer)

rules in Chinese philosophy that govern spatial arrangement and orientation in relation to patterns of yin and yang and the flow of energy (qi); the favorable or unfavorable effects are taken into consideration in designing and siting buildings and graves and furniture

(economics) the principle that when two kinds of money having the same denominational value are in circulation the intrinsically more valuable money will be hoarded and the money of lower intrinsic value will circulate more freely until the intrinsically more valuable money is driven out of circulation; bad money drives out good; credited to Sir Thomas Gresham